Useful articles from various thermoplastic resins have been prepared from molds for many years. Injection molding provides a convenient way for preparing various articles from thermoplastic resins, particularly objects of a relatively intricate nature. In order to injection mold articles in an economic manner the mold resident cycle time should be kept to a minimum. This shorter cycle time provides a shorter resin heat period with consequently less thermal damage to the resin itself and/or less thermal promoted interaction between the resin and various additives present in the resin. In order to accomplish a release of the resin from the mold, various mold release agents have been found which provide for a release of the resin with lower ejection pressure. Such an agent should be chemically compatible with the resin as measured by the usual characteristics of the resin under normal conditions and heat treatments.
Of the thermoplastic resins which find a mold release agent useful from time to time one of the most sensitive to chemical interaction are the polycarbonates. The carbonate bond is susceptible to bond cleavage, for example, hydrolysis from the usual sources. Therefore, the particular mold release agent in the past has been substantially neutral.
A series of patents and publications disclosing the use of carboxylic acid esters and paraffin waxes as mold release agents for polycarbonates are known.
U.S. Pat. No. 3,836,499--polycarbonate molding compositions having as a mold release additive an ester of a saturated aliphatic long chain monocarboxylic acid and a univalent aliphatic long chain alcohol.
U.S. Pat. No. 4,097,435--polycarbonate molding compositions including glass fibers, and an ester wax of montanic acid as a mold release additive. Example 2 uses the stearyl ester of behenic acid.
U.S. Pat. No. 3,784,595--polycarbonate molding compositions having as a mold release additive an ester of a trihydric alcohol and a C.sub.10 to C.sub.22 saturated aliphatic carboxylic acid.
U.S. Pat. No. 4,065,436--polycarbonate molding compositions having as a mold release additive an ester of a saturated aliphatic carboxylic acid with 10 to 20 carbon atoms per molecule and an aromatic hydroxy compound with from 1 to 6 hydroxyl groups.
U.S. Pat. No. 4,131,575--polycarbonate molding compositions having as a mold release additive an ester of a saturated aliphatic carboxylic acid with 10 to 20 carbon atoms and 4-hydric to 6-hydric alcohols.
Japanese No. 72 41,092--mold release agents are esters from C.sub.12-30 aliphatic monocarboxylic acids and mono or polyhydroxy aliphatic saturated alcohol. Butyl stearate is a specific example. Stearnic acid is also employed in combination with polycarbonate.
U.S. Pat. No. 3,186,961--discloses many esters which can be used in polycarbonate as plasticizers.
U.S. Pat. No. 4,082,715--discloses use of esters in polycarbonate and shows the plasticizing ability of various esters.
Japanese Nos. 79 76,651; 79 16,559; and 80 84,353--all of these laid open patent applications disclose polycarbonate or polyestercarbonate with paraffin waxes.